The arms are Or, two camellias Gules leaved Vert ordered per fess, in between a cape Azure torn and open, in base a triple mount Vert issuant. Mural crown argent with three visible towers (village rank) and white scroll reading in black upper case letters "SINTRA - S. MARTINHO"
Meaning:
The blue coat, nearly divided into two halves, represents St. Martin, who shared his blue coat with a beggar. (The blue coat is also a constituent of the French flag, St. Martin was Bishop of Tours)
Source: I spotted this flag in front of the administration building in São Martinho on 6 October 2013.
Klaus-Michael Schneider, 25 July 2014

Published in Diário da República: III Série on 17 January 2001
Klaus-Michael Schneider, 25 July 2014

Presentation of São Martinho

São Martinho Commune was one of the pre-2013 communes of Sintra Municipality (q.v.); it had 6226 inhabitants in 2011 and covered 24.3 km².
Klaus-Michael Schneider, 25 July 2014